Wave length modulation



Feb. 8, 1944. R. E. SCHOCK 25341,243-

wAvE LmTH MobULAT-IoN Original Filed July 18, 1940 ZASheetS-Sheet 1 lNvEN-roR leoerZ-Ef.

- A TITORNEY Feb 8 1944 R. E. sc :HocK i 2,341,243

i wAvE LENGTH MoDULATloN original Filed July 18, 1940 2 lsheets-Sheet 2 Mge ozq-gzrazow ATTORNEY Patented Feb. s, 1944` wAvE LENGTH MoDULA'rioN noten, E. sehdek, Riverhead, N. Y., assigner to v Radio Corporation oi' America, a corporation of Delaware Original application July y 18, 1940, Serial No.

346,079, now Patent No. 2,310,260, dated February 9, 1943. Divided and this application February 27, 1942, Serial No. 432,609

4 Claims.

`This application describes a method of and means for balancing out the amplitude modulation, which is often impressed on a carrier wave at the time it is being wave-length-modulated, and is a division of my United States application No. 346,079, filed July 18, 1940, now U. S. Patent 2,310,260, dated February 9, 1943.

In describing my invention, reference will be made to the attached drawings wherein:

Figs. 1, 1a, 2, and 2a each illustratev a wave length modulator with wave amplitude mod ulation compensating means.

An arrangement of my novel means to produce wave length modulation of wave energy and at the same time correct inherent amplitude modulation thereof will now be described.

In the circuit of Fig. 1 tube 90 is an oscillator tube having its anode 92, grid 94, and cathode 96 coupled in regenerative circuits comprising an inductance |00, a variable capacity |02, and a resistance |04 shunted by a condenser |06. The elements and |02 comprise the tank circuit ulation which is introduced on the signal during `the frequency modulating process.

In operation, a modulating voltage impressed on the control grid IIB of tube ||2, Fig. 1, causes a modulation of the wave length of the oscillator including 'tube 90. It has also been found that when the conductance of the reactance tube |I2 is increased by any instantaneous value of modulating voltage, the oscillator output is at the same instant somewhat diminished, and vice versa. If, at the same instant, a portion of the modulation voltage-same polarityis fed to the control grid 49 of amplier tube 50 from potentiometer |22 as shown in Fig. 1, the gain of this amplifier will increase when the oscillator output is decreasing and -vice versa.. The amount of this change of gain may be so adjusted that-com plete compensation is made for the amplitude and the elements |04 and |06 comprise the conv sired amplitude modulation thereof during thegrid ||8 is connected to a point on this phase shifting circuit to be excited by a voltage displaced in phase by about 90 degrees relative to the radio-frequency voltage on plate 92 of the oscillator tube 90.

By controlling the conductance of the reactance tube ||2 the reactive effect Atherein is controlled to control the tuning of tank circuit |00, |03. 'I'his is done by modulating potentials from |20. The operation oi this type of wave length modulator is now well imderstood, and additional description here is believed unnecessary.

The oscillator feeds an ampliner tube 50 by way of. a coupling and blocking condenser 54, and

.the plate circuit' 55 0f tube 50 is, in this case,

tuned to the oscillator frequency.

' Potentiometer |20 is a. means of controlling the modulation input voltage to the reactance modulator tube H 2, and potentiometer ||2 is a means of controlling the amount of modulation voltage fed to the control grid 49 of amplier tube 501er the purpose of producing amplitude modulation and thereby removing undesired amplitude modmodulation present.

In Fig. 1a, the compensating modulation voltage is supplied from a transformer 60 to the two potentiometers |20 and |22. Modulation potential of one phase is supplied to the grid ||8 of reactance tube ||2 as in Fig. 1. Here, however, the compensating modulation potential is supplied to the grid H3 of a tube the anode of which is connected to the anode 91 of the tube 90 and to a. common plate potential supply choke lll. In this manner, the oscillator tube 90 is plate-modulated in a direction to oppose undewave length modulation process accomplished by the reactance tubel l2.

' Thecircuit ot Fig. 2 is similar to that of Fig. 1

`except for the method of obtaining compensating or balancing voltage to apply to the grid of ampliier tube 50. Here the amplitude modulapotentiometer 'I0'.

'The modulator of Fig. 2 may be modied as shown in Fig. 2a. In this modication, tubeA I has its grid IIS coupled to a point on resistance '10' to be excited by the compensation control potential. Tube amplifles the control potential and derives its plate current from choke Ill which also supplies plate current to the plate of the oscillator tube 90. The oscillator is platetions in a direction to compensate amplitude modulation thereof in an undesired manner durf ing the frequency modulation process.

What is claimed is: .1. In a. wave length modulation system, an

oscillation generator comprising an electron disd charge device having its electrodes connected in oscillation generating and frequency determining circuits, a reactance tube having electrodes connected in shunt to. a portion at least of said oscillation1 generating circuits, said reactance tube having two electrodes excited in phase dis'- placed relation by generated oscillations whereby said tube is caused to act as a reactance forming part' of said oscillation generating circuits, an oscillation amplifier tube having input electrodes coupled to said oscillation generating circuits and having .output electrodes coupled to an output I circuit, `andconnections for modulating the impedance ofsaid reactance tube andthe imvpedance of said ampliiier tube in accordance with control potentials.

2. In a wave length modulation system, an oscillation generator comprising an electron discharge device having itselectro'des connectedin oscillation generating andfrequency determining circuits, a reactance tube having electrodes connected in shunt to a portion at least of said oscillation generating circuits, said reactance tube having two electrodes excited in phase disl.

placed relation by generated oscillations whereby said tube is caused to act as a reactance torming part o! said oscillation generating circuits,

a radio frequency amplifier tube having input electrodes coupled to said oscillation generating circuits and having output electrodes connected in an output circuit, and connections for modu-l lating the gain of said reactance tube and the gain of said amplifier tubefin accordance with control potentials.

3. In a frequency modulation system1 an oscillation generator comprising an electron discharge device having its electrodes connected in oscillation generating and frequency determining circuits, a reactance tube having an anodeand a cathodeconnected to spaced points on said oscillation generating circuits. said tube having a control grid coupled to said generating circuits and excited by generated oscillations in phase displaced relation with respect to the excitation of `said anode by said generated oscillations whereby said tubeis caused to act as a reactance escasas a control grid and cathode coupled to said oscilcircuit determining in part at least the timing oi' the wave energy ilowing in said tuned circuit, a

reactance tube having an electron receiving electrode, a cathode,` and a control electrode, connections for -impressing voltages from said tuned circuit on the electron receiving electrode oi' said reactance tube, connections for impressing voltages from said tuned circuit on the control electrode of said reactance tube, said impressed voltages being displaced substantially 90 degrees,

whereby a reactive effect isl produced in said ref actance tube, connections coupling the impedance between two electrodes of said reactance the supplemental reactance supplied to said tuned 1 circuit tomodulate the timing Vof tlfe wave energy owing therein, and means for compensating for amplitude modulation'produced during 'said timingmodulation comprising a modulation potential ampliiier tube having an anode, a i cathode and a control grid. a modulation poten- 40 tial impedance coupling the anode of said amplier tube to the cathode of said amplier tube, an impedance to wave energy or the frequency of i the wave energy to -be modulated coupling the anode oi said ampliiler tube to the' anode of said first tube, a coupling between the cathode of said amplifier tube and the cathode of said ilrst tube, and connections to the control grid and cathode or said amplier tube for impressing thereon potentials which .vary substantially in accord- ROBERT E. scnocl.

ance with said modulating botenualsand suba. 

